Active matrix liquid crystal display having a contact hole

ABSTRACT

An active matrix liquid crystal display (AMLCD) with a high aperture ratio and with an etch stopper formed by a back exposure method, and not with an additional pattern mask. The AMLCD has a gate line that extends in a first direction on the substrate and has a first region that corresponds to the gate electrode region. The gate line also has a second region corresponding to a non-gate electrode region and a contact hole adjacent to the first region and the second region. A thin film transistor (TFT) of the AMLCD is formed with a nonlinear channel region.

BACKGROUND OF THE INVENTION

The present invention relates to an active matrix liquid crystal display(AMLCD), in which no pattern mask is required to form an etch stopper.

A conventional AMLCD includes a large number of pixels and associatedswitching devices, such as thin film transistors (TFTs), arranged in anarray. The pixels are interconnected by a plurality of gate lines, databus lines, and pads formed at each end of the gate and data bus lines.Each pixel includes a pixel electrode, which is electrically connectedto the switching devices for applying voltages depending on whetherlight is to be transmitted or blocked by the pixel. A storage capacitoris also included to improve the pixel's electrical characteristics.

FIG. 1A is a plan view showing a first example of a conventional AMLCDhaving an etch stopper formed by a back exposure method, and FIG. 1B isa cross-sectional view along the line I--I of FIG. 1A.

As shown in FIG. 1, each pixel includes: (1) a gate line 1 and data line2, which cross each other; (2) a gate electrode 11 extending from gateline 1; (3) a semiconductor active layer 14 overlapping gate electrode11; (4) a source electrode 16 extending from data line 2; and (5) a TFT3 including a drain electrode 17 formed corresponding to sourceelectrode 16. Further, a pixel electrode 19 is connected to drainelectrode 17. Finally, an etch stopper, not shown in FIG. 1A, is formedhaving the same shape as gate line 1.

As shown in FIG. 1B, a protruding portion of the gate line serves as thegate electrode 11 of the TFT. Gate electrode 11 is formed on aninsulating substrate 10, and a first insulating layer 13 is formed on anexposed surface of insulating substrate 10. Moreover, gate electrode 11and semiconductor active layer 14 are formed overlapping the gateelectrode 11.

Further, an etch stopper is formed on semiconductor active layer 14 by aback exposure method. In this instance, the method of fabricating theetch stopper includes the steps of: forming successively an insulatinglayer and positive photoresist film on semiconductor active layer 14 andthe exposed first insulating layer; patterning the photoresist film by aback exposure process; developing the photoresist film to form aphotoresist pattern; etching the insulating layer to form an etchstopper; removing the photoresist pattern.

Next, an ohmic contact layer 6 is formed on portions of etch stopper 15and semiconductor active layer 14. Ohmic contact layer 6 does notconstitute part of the channel. A source electrode 16 is then formed onsemiconductor active layer 14, partially overlapping gate electrode 11.In addition, a drain electrode 17 is formed partially overlapping gateelectrode 11 and symmetrically with source electrode 16. Then, a secondinsulating layer 18 is formed on source/drain electrodes 16 and 17 toprotect insulating substrate 10. Pixel electrode 19 is then formedconnected to drain electrode 17 through a contact hole formed in thesecond insulating layer 18. Gate electrode 11 may be formed of aconductive material capable of anode-oxidation. This material choiceallows an oxide insulating layer 12 to be formed on a surface of gateelectrode 11.

As described above, in a conventional AMLCD, the etch stopper is formedeasily without preparing a pattern mask. This AMLCD does not improve theaperture ratio, however, because the gate electrode protrudes beyond thegate line.

FIG. 2A is a plan view showing a second example of the conventionalAMLCD. The etch stopper in this example was formed using a pattern mask.FIG. 2B is a cross-sectional view taken along the line II--II of FIG.2A.

As shown in FIG. 2A, a mostly linear gate line 22 is provided on aninsulating substrate, and a data line 21 is provided crossing gate line22. Data line 21 has a protruding portion 23 extending in the samedirection as gate line 22. A drain electrode 24 is formed incorresponding relationship to a source electrode, which includesprotruding portion 23 at one side of data line 21 and an inner portionlateral of data line 21. Drain electrode 24 is connected to an upperportion of pixel electrode 29. Here, drain electrode 24 overlaps part ofgate line 22 and is formed at an equally spaced distance from the sourceelectrode. The protruding portion of adjacent data line 21, drainelectrode 24, and semiconductor island-shaped active layer 27 are formedsuch that the angle between the drain electrode and a channel region ofthe TFT is non-linear or L-shaped. As a result, current flows from theentire source electrode. Further, since the channel length can beincreased, it is possible to reduce the physical size of the sourceelectrode while maintaining the same level of current flow as in thegeneral conventional TFT. A reduction in the source electrode's physicalsize lessens the amount of source-gate electrode overlap and thus theresulting capacitance C_(gs) can also be reduced. Moreover, since thestructure of gate line 22 is almost linear, the aperture ratio isincreased.

As shown in FIG. 2B, a gate electrode of mostly linear gate line 22 isformed on an insulating substrate 20, and a first insulating layer 26-1is formed on an exposed surface of insulating substrate 10 and gateelectrode 22. Also, first insulating layer 26-1 and semiconductor activelayer 27 are formed to overlap the gate electrode 22.

In this device, a pattern mask is used to form an etch stopper 28 onsemiconductor active layer 27. The method of fabricating the etchstopper includes the steps of forming successively an insulating layerand positive photosensitive photoresist film on semiconductor activelayer 27 and the exposed first insulating layer 26-1, exposing thephotoresist film using a pattern mask, developing the photoresist filmto form photoresist pattern, and etching the insulating layer to formthe etch stopper.

Next, ohmic contact layer 25 is formed on portions of etch stopper 28and semiconductor active layer 27. Then, a source electrode 23 is formedon semiconductor active layer 28 partially overlapping gate electrode22. In addition, a drain electrode 24 is formed partially overlappinggate electrode 22. Next, a second insulating layer 26-2 is formed onsource/drain electrodes 23 and 24. A pixel electrode 29 is formed andconnected to drain electrode 24 through a contact hole in the secondinsulating layer 26-2. In this instance, gate electrode 22 may be formedof a conductive material capable of anode-oxidation. This materialchoice allows an oxide insulating layer 22-1 to be formed on a surfaceof gate electrode 22.

While this second AMLCD example also has an improved aperture ratio dueto the gate line's almost linear structure, it requires using a patternmask to form the etch stopper. This requirement adds complexity andadditional cost to the AMLCD fabrication process. For this reason, aneed exists for an AMLCD fabrication method which permits forming anetch stopper without the additional complexity of first forming apattern mask on the substrate layer.

SUMMARY OF THE INVENTION

Accordingly, it is a goal of the present invention to provide an AMLCDin which an etch stopper is formed without first preparing a patternmask, and in which the aperture ratio is increased.

Additional advantages of the invention will be set forth in part in thedescription which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. Theadvantages of the invention may be realized and obtained by the elementsand combinations particularly pointed out in the appended claims and thedrawings.

To achieve these and other advantages and in accordance with thisinvention, as embodied and described herein, there is provided an activematrix liquid crystal display (AMLCD) including: an insulatingsubstrate; a gate line extending in a first direction on the substrateand having a first region corresponding to gate electrode region, asecond region corresponding to a non-gate electrode region, and acontact hole adjacent to the first region and the second region, thegate line exposing a portion of the substrate; a first insulating layerformed on the gate line; an island-shaped semiconductor active layerformed above and overlapping the first region and a portion of thecontact hole of the gate line; an etch stopper formed on semiconductoractive layer and exposing a portion of the semiconductor active layer; adata line formed on the substrate crossing the gate line and having afirst portion, a protruding portion, extending in the first directionabove the first region of the gate line and connecting the exposedportion of the semiconductor active layer as a source electrode, and asecond portion contiguous with the protruding portion, the first andsecond portions of the data line overlying the gate line; and a drainelectrode formed corresponding with the source electrode.

In another aspect, there is provided a method of fabricating an AMLCDincluding the steps of: providing a first conductive layer on asubstrate surface; patterning the first conductive layer to form a gateline extending in a first direction on the substrate surface and havinga first region corresponding to gate electrode region, a second regioncorresponding to a non gate electrode region, and a contact holeadjacent to the first region and the second region, the gate lineexposing a portion of the substrate; forming an insulating layer on thefirst conductive layer and the exposed portion of the surface of thesubstrate; forming an amorphous silicon layer on the insulating layer;patterning the amorphous silicon layer to form a semiconductor activelayer overlapping the first region and a portion of the contact hole ofthe gate line, and exposing a portion of the first insulating layer;forming an insulating layer on an exposed surface of the firstinsulating layer and on the semiconductor active layer; patterning theinsulating layer to form an etch stopper having the same shape as thegate line, exposing a portion of the semiconductor active layer; forminga second conductive layer on the substrate; and, patterning the secondconductive layer to form a data line on the substrate.

According to a still further aspect of the invention, there is providedan active matrix liquid crystal display (AMLCD) including: an insulatingsubstrate; a gate line extending in a first direction on the substrateand having a first region corresponding to gate electrode region, asecond region corresponding to a non-gate electrode region, and acontact hole adjacent to the first region and the second region, thegate line exposing a portion of the substrate; a first insulating layerformed on the gate line; an island-shaped semiconductor active layerformed above and overlapping the first region and a portion of thecontact hole of the gate line; a data line formed on the substratecrossing the gate line and having a first portion, a protruding portion,extending in the first direction above the first region of the gate lineand connecting the exposed portion of the semiconductor active layer asa source electrode of a TFT, and a second portion contiguous with theprotruding portion, the first and second portions of the data lineoverlying the gate line; and a drain electrode formed corresponding withthe source electrode, the contact hole of the gate line providing thatthe R/C-type delay of the gate line and the turn-on time of the TFT arereduced.

Both the general description and the following detailed description areexemplary and explanatory only and do not restrict the invention asclaimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate a presently preferred embodimentof the invention and together with the description, serve to explain theprinciples of the invention.

In the drawings:

FIG. 1A is a plan view of a first example of the conventional AMLCD;

FIG. 1B is a cross-sectional view taken along the line I--I of FIG. 1A;

FIG. 2A is a plane view of a second example of the conventional AMLCD;

FIG. 2B is a cross-sectional view taken along the line II--II of FIG.2A;

FIG. 3A is a plan view of an embodiment of an AMLCD in accordance withthe present invention;

FIG. 3B is a cross-sectional view taken along the line III--III of FIG.3A;

FIGS. 4A-4E are cross-sectional views taken along the line III--III ofFIG. 3A and illustrating a manufacturing process in accordance with thepresent invention; and

FIGS. 5A-5B are cross-sectional views taken along the line III--III ofFIG. 3A and illustrating another manufacturing process in accordancewith the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

FIG. 3A is a plan view of an embodiment of an AMLCD in accordance withthe present invention, in which an etch stopper is formed. In accordancewith the first embodiment, a contact hole, T, of appropriate size isformed within a gate line 32, which serves as a back exposure mask forforming an etch stopper.

Preferably, gate line 32 having contact hole T and a protruding portionis formed on an insulating substrate. The contact hole and semiconductoractive layer 36 divides gate line 32 into a gate region and a non-gateregion. Next, a data line 31 is formed across the gate line 32. Dataline 31 has a protruding portion 33 which includes the source electrode.The protruding portion 33 includes an inner lateral portion of data line31 and covers a portion of the contact hole T of gate line 32. Inaddition, the protruding portion 33 is positioned in the same directionas the gate line 32 and overlaps a portion of the gate line 32.Protruding portion 33, i.e., the source electrode, covers the exposedsemiconductor active layer 36 through the contact hole of the etchstopper.

As shown in FIG. 3A, a drain electrode 34 is disposed symmetrically withprotruding portion 33 and the source electrode, or inner lateralportion, of data line 31. Moreover, a pixel electrode 39 is connected tothe drain electrode 34. Preferably, drain electrode 34 and the sourceelectrode are composed of the same material.

In this embodiment, the present invention has protruding portion 33which extends from data line 31 and partially overlaps gate line 32adjacent protruding portion. However, to improve the aperture ratio theinvention contemplates forming gate line 32 in a straight line ratherthen forming one with a protruding portion.

FIG. 3B is a sectional view taken along a line III--III of FIG. 3A. Inthis figure, the source electrode 33 and the drain electrode 34 areformed on an ohmic contact layer 40 which covers portions of an etchstopper 37 and a semiconductor active layer 36. In turn, semiconductoractive layer 36 is on a first insulating layer 35-1 and overlaps a gateregion 32-1 of the gate line 32. In this manner, the gate region 32-1,which is part of the gate line 32 under the source electrode 33, drainelectrode 34, and the semiconductor active layer 36 form a TFT toperform a switching function.

As seen in FIG. 3A, a bent channel region is formed in the semiconductoractive layer 36. The drain electrode 34 is connected through a contacthole in a second insulating layer 35-2 to the pixel electrode 39.Preferably, gate line 32 with gate electrode region 32-1 and non-gateelectrode region 32-2 comprise a conductive material capable ofanode-oxidation. This material choice allows an oxide insulating layer38 to be formed on a surface of gate line 32.

FIGS. 4A-4E show steps of a method of fabricating an AMLCD consistentwith this embodiment of the present invention. In addition, FIGS. 4A-4Eare progressive sectional views taken along the line III--III of FIG.3A.

First, as shown in FIG. 3A, a first conductive material layer issputtered onto a transparent and insulating substrate 30. The firstconductive material is then patterned to form a gate line 32 in which acontact hole T is made. Contact hole T divides the portion of the gateline into two regions 32-1 and 32-2. One region 32-1 will become a gateelectrode region and the other region 32-2 will become a non-gateelectrode region in the completed device. Preferably, the firstconductive material is selected from the group including aluminum (Al),aluminum alloy, molybdenum (Mo), molybdenum alloy, or any otheranode-oxidizable metal.

After forming the two regions, an anode oxidation process is carried outon the surface of the gate line 32 to form an anode oxidation layer 38.Next, as shown in FIG. 4B, a first insulating layer 35-1 and anamorphous silicon layer 36a are successively formed. In the preferredembodiment, a first insulating layer 35-1 is formed by providing asilicon oxide layer or a silicon nitride layer on the exposed surfacesof the oxide insulating layer.

Then, the amorphous silicon layer 36a is patterned with an etchingprocess to form semiconductor active layer 36. This layer overlaps onlythe upper portions gate electrode region 32-1 and a portion of contacthole T of the gate line 32.

Referring to FIG. 4C, an insulating layer 37a for etch stopper, such assilicon nitride, is formed on the semiconductor active layer 36 and onthe exposed portion of the first insulating layer 35-1. Next, a backexposure step is performed to create an etch stopper 37 on thesemiconductor active layer 36 and on the exposed portion of the gateinsulating layer 35-1. As a result, the etch stopper 37 has a contacthole at the same position as gate line 32. Accordingly, etch stopper 37exposes the portion of semiconductor layer 36 overlapping the contacthole in gate line 32.

In this embodiment, the etch stopper is formed with a known backexposure method. In this method, the insulating layer and a positivephotosensitive photoresist film are successively formed on thesemiconductor active layer 36 and the exposed first insulating layer35-1. As a result, a photoresist pattern having the same shape as gateline 32 can be formed because the back exposure is performed using anopaque region, gate line 32, as a mask. In turn, using the photoresistpattern to form the etch stopper produces an etch stopper with the sameshape as gate line 32. Accordingly, in this embodiment, the presentinvention allows the etch stopper 37 to be formed without using apattern mask.

Next, as shown in FIG. 4D, a doped amorphous silicon layer 40 and asecond conductive material layer 33, 34 are successively formed on theetch stopper 37, the exposed semiconductor active layer 36, and theexposed first insulating layer 35-1. Then, second conductive materiallayer and doped amorphous silicon layer are patterned to form a dataline having a source electrode 33 and a drain electrode 34. Here, thepatterned doped amorphous silicon layer becomes ohmic contact layer 40and serves to reduce the contact resistance with semiconductor activelayer 36.

After this step, the source electrode 33 is provided in an area asdefined by the protruding portion of data line 31. Preferably, theprotruding portions of data line 31 are angled or L-shaped such that anangled channel area can be obtained (as shown in FIG. 3A).

Referring to FIG. 4E, second insulating layer 35-2, preferably includingsilicon oxide and silicon nitride layers, is formed on the remainingexposed surfaces by sputtering or a chemical vapor deposition (CVD)method. Next, contact holes are formed by dry-etching the secondinsulating layer 35-2, thereby exposing a portion of drain electrode 34.Finally, a transparent conductive material, preferably, indium tin oxide(ITO), is deposited, and subsequently patterned to form a pixelelectrode 39 which contacts the drain electrode 34 through the contacthole.

In another embodiment, the present invention not only has the advantageof creating the etch stopper by back exposure without any additionalmask patterns, but also has the advantage of a high aperture ratio, ascompared with the conventional AMLCD.

FIGS. 5A-5B show steps of a method of fabricating an AMLCD in accordancewith a second embodiment of the present invention taken along the lineIII--III of FIG. 3A.

The etch stopper, which is produced as shown in FIGS. 4A-4E, is formedwith the same shape as the gate line. But, the etch stopper can beformed only on a semiconductor active layer because the etch stopper'sfunction is to prevent the etchant from over etching the semiconductoractive layer which is formed of amorphous silicon.

First, as shown in FIG. 4A and described above, the gate line havinggate electrode region 32-1, non gate electrode region 32-2 and a contacthole, and the anode oxide layer 38 are formed on the insulating andtransparent substrate 30.

Next, as shown in FIG. 5A, a first insulating layer 35-1, an amorphoussilicon 36a and an insulating layer for an etch stopper, such as siliconnitride layer, are successively formed. Then, using a back exposuremethod, the insulating layer is etched to form an etch stopper 37.

In this embodiment, the etch stopper is formed with a back exposuremethod. In this method, the insulating layer used for the etch stopperand a positive photosensitive photoresist film are successively formedon the semiconductor active layer 36 and the exposed first insulatinglayer 35-1. As a result, a photoresist pattern having the same shape asgate line 32 can be formed because the back exposure is performed usingan opaque region, gate line 32, as a mask. In turn, using thephotoresist pattern to form the etch stopper produces an etch stopperwith the same shape as gate line 32. Accordingly, in this embodiment,the present invention allows the etch stopper to be formed without usinga pattern mask.

Next, as shown in FIG. 5B, the etch stopper with the same shape as gateline 32 is etched to form an etch stopper with the same shape as onlythe gate electrode region 32-1 of the gate line 32. This etch stopper 37is produced with the mask having the pattern of the gate electroderegion of gate line 32. Amorphous silicon layer 36a is patterned to forma semiconductor active layer 36. This region is defined as shown in FIG.3A.

Finally, as described by the general processes outlined in FIGS. 4D-4E,ohmic contact layer, data line having source electrode, drain electrode,second insulating layer, and pixel electrode are successively formed.

As described above, in the AMLCD of the present invention, the apertureratio increases by forming a TFT above the gate line and providing anonlinear channel area. In contrast to conventional fabricationtechniques, the channel region is formed in a non-straight line andtherefore, the length of the channel is extended. Consequently, ascompared with a TFT having the same channel length, the parasiticcapacitance generated between the gate line and the drain electrode canbe reduced significantly.

Further, in the case where a contact hole is formed within the gateline, an etch stopper can be formed by using the previously formed gateline as a mask, without first preparing a pattern mask. This advantagegreatly improves and simplifies the fabrication process.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and illustrated examples shown anddescribed herein. Accordingly, various modifications may be made withoutdeparting from the spirit or scope of the general inventive concept asdefined by the appended claims and their equivalents.

What is claimed is:
 1. An active matrix liquid crystal display (AMLCD)comprising:an insulating substrate; a gate line extending in a firstdirection on said substrate and having a first region corresponding to agate electrode region, a second region corresponding to a non-gateelectrode region, and a contact hole adjacent to said first region andsaid second region, said gate line exposing a portion of said substrate;a first insulating layer on said gate line; an island-shapedsemiconductor active layer above and overlapping said first region and aportion of said contact hole of said gate line; an etch stopper onsemiconductor active layer and exposing a portion of said semiconductoractive layer; a data line on said substrate crossing said gate line andhaving a first protruding portion extending in said first directionabove said first region of said gate line and connecting said exposedportion of said semiconductor active layer as a source electrode, and asecond portion contiguous with said protruding portion, said first andsecond portions of said data line overlying said gate line; and a drainelectrode disposed in correspondence with said source electrode.
 2. TheAMLCD according to claim 1, wherein said first portion of said data lineis defined as a source electrode including an inner portion spacedlaterally from said data line.
 3. The AMLCD according to claim 1,wherein said etch stopper has the same shape as said gate line.
 4. TheAMLCD according to claim 1, wherein said etch stopper has the same shapeas said first region of said gate line.
 5. The AMLCD according to claim1, wherein said gate line is linear and has a substantially uniformwidth.
 6. The AMLCD according to claim 1, wherein said gate line has aprotruding portion partially overlapping said drain electrode and oneside of said source electrode.
 7. The AMLCD according to claim 1,wherein said source electrode and said drain electrode define an angledchannel region of a thin film transistor (TFT).
 8. The AMLCD accordingto claim 1, wherein said etch stopper has the same shape as said gateline.
 9. The AMLCD according to claim 1, wherein said etch stopper hasthe same shape as said first region of said gate line.
 10. An activematrix liquid crystal display (AMLCD) comprising:an insulatingsubstrate; a gate line extending in a first direction on said substrateand having a first region corresponding to a gate electrode region, asecond region corresponding to a non-gate electrode region, and acontact hole adjacent to said first region and said second region, saidgate line exposing a portion of said substrate; a first insulating layeron said gate line; an island-shaped semiconductor active layer above andoverlapping said first region and a portion of said contact hole of saidgate line; a data line on said substrate crossing said gate line andhaving a first protruding portion extending in said first directionabove said first region of said gate line and connecting said exposedportion of said semiconductor active layer as a source electrode of athin film transistor (TFT), and a second portion contiguous with saidprotruding portion, said first and second portions of said data lineoverlying said gate line; and a drain electrode disposed incorrespondence with said source electrode, said contact hole of saidgate line providing that the R/C-type delay of said gate line and theturn-on time of said TFT are reduced.
 11. The AMLCD according to claim10, wherein said first portion of said data line is defined as a sourceelectrode including an inner portion spaced laterally from said dataline.
 12. The AMLCD according to claim 10, wherein said gate line islinear and has a substantially uniform width.
 13. The AMLCD according toclaim 10, wherein said gate line has a protruding portion partiallyoverlapping said drain electrode and one side of said source electrode.14. The AMLCD according to claim 10, wherein said source electrode andsaid drain electrode define an angled channel region of said TFT.
 15. Anactive matrix liquid crystal display (AMLCD) comprising:an insulatingsubstrate; a gate line extending in a first direction on said substrateand having a first region corresponding to a gate electrode region, asecond region corresponding to a non-gate electrode region, and acontact hole adjacent to said first region and said second region, saidgate line exposing a portion of said substrate; a first insulating layeron said gate line; an island-shaped semiconductor active layer above andoverlapping said first region and a portion of said contact hole of saidgate line; an etch stopper on semiconductor active layer and exposing aportion of said semiconductor active layer; a data line on saidsubstrate crossing said gate line and having a first protruding portionextending in said first direction above said first region of said gateline and connecting said exposed portion of said semiconductor activelayer as a source electrode of a thin film transistor (TFT), and asecond portion contiguous with said protruding portion, said first andsecond portions of said data line overlying said gate line; and a drainelectrode disposed in correspondence with said source electrode, saidcontact hole of said gate line providing that the R/C-type delay of saidgate line and the turn-on time of said TFT are reduced.